The present invention relates to back light units using a light emitting diode (LED) as a light source, for example, and relates to video display devices using the same.
In response to a request for power-saving in recent years, there is a need for a reduction in power consumption also in the back light unit used in a liquid crystal display device. For this reason, as the light source of the back light unit, in place of a fluorescent tube, such as a conventional CCFL, a light emitting diode (LED) with a high luminous efficiency and a high responsiveness (i.e., the LED with which the area control to locally or partially control the light intensity of the back light is easy) is beginning to be used.
The types of the back light unit using an LED as the light source mainly include a direct type and an edge light type (also referred to as a side light type). The edge light type is advantageous in achieving a reduction in thickness (reduction in depth dimension) of a video display device because it has a configuration, wherein a point-like light, such as an LED, is converted into a planar light by means of a tabular light guide plate comprising a transparent resin and emitted to a liquid crystal panel.
As the prior art for the back light device using such a light guide plate, the one described in JP-A-2006-236701 is known, for example. JP-A-2006-236701 discloses a back light device wherein a plurality of recesses are vertically provided in the bottom surface of a light guide plate, with the horizontal direction taken as the longitudinal direction, wherein a plurality of side emission type LEDs are housed in each recess, and wherein the light from the LED is reflected inside the light guide plate and emitted to a liquid crystal panel side.